1. Field of the Invention
The present invention relates generally to pressure sensors and, more particularly, to a flowthrough pressure sensor which permits the use of materials approved by the Federal Food and Drug Administration in applications where the pressure of body fluids are to be measured.
2. Description of the Prior Art
Various types of pressure sensors are known to those skilled in the art. For example, U.S. Pat. No. 5,042,495, which issued to Spotts et al on Aug. 27, 1991, discloses a pressure sensor which comprises a first housing piece defining a lumen therethrough and an opening to the lumen to provide communication between it and a sensing element. The housing piece has a first surface surrounding its opening. A second housing piece is shaped for mating with the first housing piece and provides a region for containing a sensing element in position to communicate with the lumen via its opening. The second housing piece has a second surface that surrounds the region. It faces and conforms to the shape of the first surface. Also disclosed are insulation displacement blades to provide electrical connection between a sensing element and a wire and a compressed elastomeric displacement ceiling ring filled with gel and providing a communication path between the opening and the sensing element.
U.S. patent application Ser. No. 07/962,641 (M10-14882) was filed on Oct. 16, 1992 by Maurer and assigned to the assignee of the present application. It describes a pressure transducer which has a housing member that attaches to a rigid and generally planar member, such as a ceramic circuit board. The legs of the housing member can pass through holes in the circuit board or, alternatively, attach to the edges of the circuit board. The legs of the housing are provided with bails which have steps that are shaped to cease the circuit board after the legs are flexed to permit insertion of the board between them. The housing is provided with an opening that is shaped to receive a media seal, a pressure sensor die and a conductive seal between a surface of the opening and a surface of the ceramic circuit board. When the circuit board is attached to the housing, the seals and the pressure sensor die are compressed therebetween to provide good fluid sealing association between the components and to also provide electrical communication between components on the pressure sensor die and components on the circuit board. An alternative embodiment of the device comprises two housing members that are attached to opposite sides of the same circuit board so that a differential pressure can be measured.
U.S. Pat. No. 4,656,454, which issued to Rosenberger on Apr. 7, 1987, describes a low cost piezoresistive pressure transducer that utilizes premolded elastomeric seals and is adapted for automatic assembly. It also describes a method of producing the transducer. The piezoresistive stress sensitive element is in the form of a diaphragm of semiconductor material having a thickened rim. The element is held at its rim between a pair of premolded elastomeric seals in a thermoplastic housing. Electrical connections with external circuitry are made with strain relief jumpers which connect conductive regions on the element outside the seals to conductors which pass through the housing wall.
U.S. Pat. No. 5,184,107, which issued to Maurer on Feb. 2, 1993, discloses a low cost piezoresistive pressure transducer which utilizes premolded elastomeric seals in which at least one seal is electrically conductive. A piezoresistive stress sensitive element in the form of a diaphragm of semiconductor material having a thickened rim is held at its rim between a pair of premolded elastomeric seals in a two-piece housing. Electrical connections with external circuitry are made by conductive paths through one of the elastomeric seals which makes contact with electrical leads which pass through the housing wall.
U.S. Pat. No. 5,257,547, which issued to Boyer on Nov. 2, 1993, discloses an amplified pressure transducer which incorporates numerous stress reducing characteristics. A pressure sensor is mounted to a ceramic plate with a buffer plate therebetween in order to isolate the pressure sensor from stresses that could be transmitted through the ceramic plate. The ceramic plate is necessary for the purpose of supporting a plurality of electronic components which comprise an amplification and compensation circuit. The ceramic plate is separated from all parts of its housing accept a minimal central surface on a support boss which provides the support for the pressure sensitive device.
When flowthrough pressure sensitive devices are used to measure the pressure of body fluids, such as during kidney dialysis procedures, the pressure sensor must exhibit certain required characteristics. For example, the Federal Food and Drug Administration requires that the materials used in a pressure sensor of this type be certified as being acceptable for this type of use. In addition, if the device is intended for repeated uses the application of a pressure sensor in this type of procedure requires that the pressure sensor be designed in such a way that small crevices and spaces be avoided. By designing the pressure sensor in this manner, it can be reused following a thorough cleaning by flushing specified fluids through the system. If the pressure sensor has crevices or small spaces within its structure, the cleansing fluid may not be able to properly remove possibly hazardous bacteria from the device following its use.
It would therefore be significantly beneficial if a flowthrough pressure transducer could be developed in which the structure avoids the presence of crevices and small spaces where bacteria-laden material can accumulate and which uses materials that are approved by the Federal Food and Drug Administration.